Special Pen To Write On Flesh Side; Particularly On Chromexcel Tan?

[onsh]

I'd like to be able to write little notes on scraps of leather to give to customers...I've tried using a sharpie, and while it works for a while, it gets gummed up quickly, particularly on a chromexcel type leather (works fine on straight veg tan, of course, but the waxes/etc make it worthless far too quickly).

There's got to be some sort of pen/something that will consistently write on leather; what am I missing?

[onsh]

and I've seen things like "leatherpen.com", but those are paint pens, and take too long to dry/too slow to write...